JP 2014-34376A discloses a vehicle power supply system in which two storage batteries are connected via a connection switch. In this vehicle power supply system, while regenerative power generation is performed, a regulated voltage of an alternator is controlled to be higher than its output voltage generated while the regenerative power generation is not performed. In addition, while regenerative power generation is performed, a target voltage of a lead storage battery is set, and then control is performed so that a deviation between a detected value and the target voltage is lower than or equal to a predetermined amount and the regulated voltage is not higher than the target voltage by a predetermined voltage width or more.